Conventionally, ischemic heart diseases are generally treated by percutaneous transluminal cornary angioplasty (PTCA), that is, a procedure of introducing a balloon catheter to, for example, a narrowed part through a lumen of a blood vessel and, after that, inflating a balloon with liquid such as normal saline solution. However, this procedure has a problem of high possibility that an acute phase block of a coronary artery is caused and that the portion treated by PTCA is narrowed again (so-called post-PTCA restenosis). To solve the problem, intraluminal graft called stent has been developed. The stent recently rapidly came into practical use and are in widespread use. According to recent data, nearly 75% of procedures using balloon catheters have been already replaced by procedures using stents.
Stent matrix is an intraluminal graft which is implanted into a portion of a lumen to be treated through the lumen of a blood vessel or the like and is increased its diameter at the portion of the lumen to be treated so that the lumen is supported by action on the inside. Though the stent is mainly used in procedure for coronary artery so that the following description will be made mainly as to the procedure for coronary artery, the stent can be used for other lumens of human body such as biliary duct, esophagus, trachea, prostate, urinary duct, fallopian tube, aortic aneurysm, peripheral artery, renal artery, carotid artery, and cerebral blood vessel. As the application field of stent expands more and more, it is expected that stents will be used in many procedures including dilation of the narrowed portion, aneurysm embolization, cancer therapy, and the like, particularly that importance of microscopic stents will be increased according to the use in a field of cerebral surgery.
Through the spread of procedure using stent, restenosises have been dramatically prevented. On the other hand, however, since metallic stent matrixes are foreign substances in human body, a metallic stent matrix may thrombi a patient after several weeks from insertion of the metallic stent matrix. This is because the metallic stent itself is exposed to blood, resulting in adsorption of blood proteins such as fibrinogen and adherence or agglutination of blood platelets, thus forming thrombus. Further, thrombus may be formed because blood platelets are agglutinated on the convexes and concaves of a skeleton of the metallic stent matrix. Intimal thickening of a blood vessel due to cytokine discharged from blood platelets agglutinated on the periphery of the metallic stent matrix has been also pointed out as a problem. Accordingly, JP H11-299901A discloses to coat an outer periphery of a metallic stent matrix with a flexible polymer film having a number of fine pores.
FIG. 2 is a perspective view showing such a metallic stent matrix 10 having a mesh form to be used for a stent, FIG. 3 is a perspective view showing the stent matrix of FIG. 2 in the expanded state 10′, and FIG. 4 is a perspective view showing a stent 20 comprising the stent matrix 10 of which outer periphery is coated with a flexible polymer film 19 having fine pores, and FIG. 5 is a perspective view showing the stent 20 in the expanded state,
In biological tissues, inner walls of blood vessels and the like, that is, portions to be directly in contact with blood are coated with cell layer so-called endothelial cells. Since the surfaces of the endothelial cells are covered by sugar and the endothelial cells secrete substances that inhibit activation of blood platelets such as prostaglandin, thrombus is hardly formed in biological tissues. According to the stent disclosed in the aforementioned JP H11-299901A, the outer periphery of the metallic stent matrix is coated with a polymer film, thereby promoting proper endothelium formation with tissues and reducing thrombogenic property.
In JP H11-299901A, the polymer film for coating the outer periphery of the stent matrix is formed as follows. That is, a mandrel for a cover strip is first impregnated in a polymer solution, then is dried, and is perforated. After that, the mandrel is pulled out, thereby forming a membrane cover strip (envelope-shaped cover film). A stent matrix is inserted into the envelope-shaped cover film in a state that the cover film is sufficiently expanded by sending air into the cover film. After that, the sending of air is stopped so as to shrink the cover film, thereby forming a covering membrane on the outer periphery of the stent matrix.